On 18.12.2010 23:27, Alexander Holler wrote:
gcc 4.5.1 seems to ignore (at least some) volatile definitions, avoid that as done in the kernel.
Reading C99 6.7.3 8 and the comment 114) there, I think it is a bug of that gcc version to ignore the volatile type qualifier used e.g. in __arch_getl(). Anyway, using a definition as in the kernel headers avoids such optimizations when gcc 4.5.1 is used.
Maybe the headers as used in the current linux-kernel should be used, but to avoid large changes, I've just added a small change to the current headers.
Signed-off-by: Alexander Hollerholler@ahsoftware.de
arch/arm/include/asm/io.h | 20 ++++++++++++++------ 1 files changed, 14 insertions(+), 6 deletions(-)
diff --git a/arch/arm/include/asm/io.h b/arch/arm/include/asm/io.h index ff1518e..5364b78 100644 --- a/arch/arm/include/asm/io.h +++ b/arch/arm/include/asm/io.h @@ -125,13 +125,21 @@ extern inline void __raw_readsl(unsigned int addr, void *data, int longlen) #define __raw_readw(a) __arch_getw(a) #define __raw_readl(a) __arch_getl(a)
-#define writeb(v,a) __arch_putb(v,a) -#define writew(v,a) __arch_putw(v,a) -#define writel(v,a) __arch_putl(v,a) +/*
- TODO: The kernel offers some more advanced versions of barriers, it might
- have some advantages to use them instead of the simple one here.
- */
+#define dmb() __asm__ __volatile__ ("" : : : "memory") +#define __iormb() dmb() +#define __iowmb() dmb()
+#define writeb(v,c) ({ __iowmb(); __arch_putb(v,c); }) +#define writew(v,c) ({ __iowmb(); __arch_putw(v,c); }) +#define writel(v,c) ({ __iowmb(); __arch_putl(v,c); })
-#define readb(a) __arch_getb(a) -#define readw(a) __arch_getw(a) -#define readl(a) __arch_getl(a) +#define readb(c) ({ u8 __v = __arch_getb(c); __iormb(); __v; }) +#define readw(c) ({ u16 __v = __arch_getw(c); __iormb(); __v; }) +#define readl(c) ({ u32 __v = __arch_getl(c); __iormb(); __v; })
Using the test code below [1] and then looking at the disassembly from the two tool chains gcc version 4.3.3 (Sourcery G++ Lite 2009q1-203) versus gcc version 4.5.1 (Sourcery G++ Lite 2010.09-50): Yes, without the additional dmb() the gcc 4.5.1 just creates
00000000 <main>: 0: e3a00000 mov r0, #0 4: e12fff1e bx lr
while with the additional dmb() it creates
00000000 <main>: 0: e59f300c ldr r3, [pc, #12] ; 14 <main+0x14> 4: e5932028 ldr r2, [r3, #40] ; 0x28 8: e5930028 ldr r0, [r3, #40] ; 0x28 c: e0620000 rsb r0, r2, r0 10: e12fff1e bx lr 14: 48318000
what looks correct. And 4.3.3 does the same code for both readl() versions. So:
Acked-by: Dirk Behme dirk.behme@googlemail.com
Thanks
Dirk
[1]
arm-none-linux-gnueabi-gcc -Wall -O2 -c foo.c -o foo.o arm-none-linux-gnueabi-objdump -D foo.o > foo.dis
-- foo.c -- struct gptimer { unsigned int tidr; /* 0x00 r */ unsigned char res[0xc]; unsigned int tiocp_cfg; /* 0x10 rw */ unsigned int tistat; /* 0x14 r */ unsigned int tisr; /* 0x18 rw */ unsigned int tier; /* 0x1c rw */ unsigned int twer; /* 0x20 rw */ unsigned int tclr; /* 0x24 rw */ unsigned int tcrr; /* 0x28 rw */ unsigned int tldr; /* 0x2c rw */ unsigned int ttgr; /* 0x30 rw */ unsigned int twpc; /* 0x34 r*/ unsigned int tmar; /* 0x38 rw*/ unsigned int tcar1; /* 0x3c r */ unsigned int tcicr; /* 0x40 rw */ unsigned int tcar2; /* 0x44 r */ };
#define dmb() __asm__ __volatile__ ("" : : : "memory") #define __iormb() dmb()
#define __arch_getl(a) (*(volatile unsigned int *)(a)) #define readl(a) __arch_getl(a) //#define readl(c) ({ unsigned int __v = __arch_getl(c); __iormb(); __v; })
int main(void) {
struct gptimer *gpt1_base = (struct gptimer *)0x48318000; unsigned int cdiff, cstart, cend;
cstart = readl(&gpt1_base->tcrr);
cend = readl(&gpt1_base->tcrr);
cdiff = cend - cstart;
return cdiff;
} -- foo.c --